. A handbook of cryptogamic botany. Cryptogams. OOMYCETES 333' emerge again outside the oogonial wall, but they remain closed at all points, and after a day or two perish. In the case of certain species, the- antherids never produce these pro- cesses, or the oogones may be without antherids. In other cases antherids are never produced fit all, or only by way of rare exception. In the meantime the oospheres ripen into oosperms, while the antherids, if present, perish. Pringsheim has recently endeavoured to show that impregnation takes place in certain species by the transference into the oosphe
. A handbook of cryptogamic botany. Cryptogams. OOMYCETES 333' emerge again outside the oogonial wall, but they remain closed at all points, and after a day or two perish. In the case of certain species, the- antherids never produce these pro- cesses, or the oogones may be without antherids. In other cases antherids are never produced fit all, or only by way of rare exception. In the meantime the oospheres ripen into oosperms, while the antherids, if present, perish. Pringsheim has recently endeavoured to show that impregnation takes place in certain species by the transference into the oospheres of minute portions of antheridial protoplasm moving in amceboid fashion. De Bary points out that, while Pringsheim has not actually seen this, the sole evidence trusted to is that of stained prepa- rations, which appear to exhibit open communication between antherid and oosphere, &c. In any case the observation does rjot affect those cases where antherids are either want- ing, or do not produce the penetrating tubular processes. The ripe oosperms thus parthe- nogenetically produced germinate after a period of rest varying from a few days to several months. Ger- mination takes place, as in the Peronosporese, either by means of a germ-tube, or zoospores are pro- duced. Propagation is effected by the agency of zoospores produced in special zoosporanges, and also excep- tionally by means of certain resting- cells formed by the mycele after transverse division of the hyphse (Saprolegnia). These swell out into globular form, with thick mem- branes and plentiful protoplasm, and germinate by the emission of a germ-tube, or zoospores are formed in them ('resting sporanges' of. Fig. !!gi.—A to C,Achlya racevtasa Hil'debr. At t:he end of A is an empty zoosporangCj s, with empty zoospore membranes ; at a, b, apd c, are ocgones witli antherids, a, in an earljr stage; b and c as in B, cogone with two oospheres and an antheridial tube applied to one. C, ripe oosperm. D, E, Achiya- f
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